Traumatic Brain Injury (TBI) can result in the disturbance of cognitive, behavioral, emotional, and physical functioning. Normal brain cognitive function depends on synaptic communication via neurotransmitter release. TBI can produce persistent deficits in both dopaminergic and cholinergic evoked neurotransmitter release, but the mechanisms are unknown. Neurotransmitter release at the synapse requires fusion of synaptic vesicles with the presynaptic plasma membrane. A crucial step in this process involves the assembly of a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, a highly stable, parallel four-helix bundle formed between the synaptic vesicle SNARE synaptobrevin 2 (syb2) and the plasma membrane SNAREs syntaxin 1 and synaptosome-associated protein of 25 kDa (SNAP-25). The pathology of SNARE proteins may play an important role in TBI, especially concerning neurotransmission and subsequent cognitive disturbances. Cysteine string protein alpha (CSP?) promotes SNARE-complex assembly by chaperoning SNAP-25 during synaptic activity. It has recently been discovered that lithium, at therapeutically relevant concentrations, can enhance the expression of CSP?. This represents a novel mechanism by which lithium may restore neurotransmitter release deficits after TBI. To further evaluate the role of CSP? in mediating lithium's effect on SNARE proteins and cognitive recovery after TBI, this project will evaluate lithium therapy in a CSP? transgenic mouse. The goal of this proposal is to examine SNARE-complex mechanisms of neurotransmission deficits after TBI. The overall hypothesis is that cognitive deficits following TBI may be, at least partialy, attributable to impairment in synaptic SNARE-complex formation and subsequent neurotransmitter release deficits. Specific Aim 1 will examine the effects of TBI on individual SNARE proteins, SNARE- complex assembly, and CSP?, a key regulator of SNARE-complex assembly. Specific Aim 2 will determine if increasing the expression of CSP? by lithium is associated with a restoration of SNARE-complex assembly and evoked neurotransmitter release as measured by microdialysis. Specific Aim 3 will determine if lithium can attenuate cognitive deficits after TBI. Successful completion of this project may provide evidence that SNARE-complexes are diminished after TBI and identify a novel application of lithium for the treatment of posttraumatic cognitive deficits.